Btinternet email

First posting and looking for help.
I have used various dial-up connections over the last 8-10 years with mixed responses and decided only last month it was about time I joined the broadband world and PlusNet looked to be the best option. (yet to be proved but looking good)
My questions is as follows:
I have an email address @btinternet.com and have used this since around 1996-7 with all the various dial-ups I have been with through SMTP and POP3 in Outlook (not express). I signed up to broadband and can freely download my emails from BTinternet but cannot send any. Is this something that is stopped by BT or PlusNet and is there anyway around it. My address does no receive a lot of spam and I would like to continue to make use of it.
Advice pleasetotal newbie Chris